Joaquin Phoenix has always been a lightweight actor. Am I the only one who found his turn in Gladiator almost unbearably sniveling? However, as he showed in Hotel Rwanda, he has potential when given the right material. As Johnny Cash in "Walk the Line", Mr. Phoenix does an impressive job of channeling the Man in Black on stage. The actor did all his own singing and, as the film progresses, his baritone can nearly be mistaken for the man himself. Off stage, however, Mr. Phoenix isn't given much to do. Like last year's "Ray", the film hits most of the typical biopic milestones - drug addiction, infidelity on tour, rehab, marital squabbles - but it doesn't do much new with them. As a result, Mr. Phoenix is left to do one quivering, moist-eyed scene after another as he pines after June Carter while the rest of his life falls apart.

With Reese Witherspoon in the role of June, however, it's easy to see why Johnny's so smitten. A Southern Belle is already hard to resist, but Ms. Witherspoon takes this opportunity to shine as she never has before. Freed from the saccharine cutesiness of the "Legally Blonde" films and the airheaded conventions of typical romantic comedies ("Sweet Home Alabama", "Just Like Heaven"), Ms. Witherspoon does her best work here. She pays tribute to June while making her a real woman with a complex set of emotions. Her attraction to Johnny, which always seems to happen at the wrong time, is the film's emotional core, and Ms. Witherspoon makes it work.

The actress also did her own singing and, like her co-star, she fares surprisingly well. Both actors are in luck, since the characters they play aren't known to have perfect singing voices. It's their charisma as much as their pitch that made them famous, and as long as the script, which director James Mangold co-wrote with Gill Dennis, keeps them on stage, the film is a joy.

There are some cute cameos throughout the film which give it period authenticity, particularly on a tour which - with artists such as Elvis Presley and Jerry Lee Lewis performing alongside Johnny and June - was the Lollapalooza of its time. Mr. Mangold has a series of competent, if slightly less than thrilling, films to his credit including "Identity", "Kate & Leopold", "Girl, Interrupted" and "Cop Land". "Walk the Line" will fit well on that list. The script is a little too "PG-13" and rote for the Man in Black. The film is worth seeing for the performances of its two leads, but as a tribute to Johnny Cash, "Walk" toes the line.